On-line film fluorination method

Abstract

An on-line film fluorination apparatus cooperative with a continuous polymer film extruding apparatus is set forth. In the preferred and illustrated embodiment, a continuous feed film is introduced into a closed cabinet or housing having alignment and guide rollers for directing the film into the housing. The film passes around a first roller having a portion thereof formed of sintered nickel to enable gaseous impregnation of the surface of the film with a gas flow including fluorine. The gas acts on the exposed face of the film, changing the surface of the polymer film, thereby providing a relatively thick surface upgrading of the film. After exposure to the fluorine, the film passes a closed vacuum container having an open face adjacent to the film surface for drawing off unreacted fluorine for recapture and recycling. This procedure can be optionally repeated on both surfaces of the film; the film that emerges from the closed cabinet or housing has a modified surface, and the cabinet or housing is evacuated with slight negative pressure.

What is claimed is: 
     
       1. A method of fluorination of a continuous extruded polyethylene film having at least a specified width comprising the steps of: (a) continuously feeding the polyethylene film after formation along a fixed path wherein the film is deployed to a specified width and travels along such a path;   (b) passing the film around a pervious means comprising a curving film contact surface and the film wraps at least partially therearound; and the surface spans the width of the film;   (c) injecting under positive pressure a flow of gas including gaseous fluorine mixed with an inert gas through said pervious means to impinge on the surface of the film to fluorinate the film to thereby change the surface characteristics of the film;   (d) moving the film past said pervious means in the presence of a continuous flow of fluorine to thereby treat a specified length of film;   (e) wherein the step of exposing said film to fluorine occurs in an isolated atmosphere subject to evacuation of surplus fluorine or fluorine compounds from the isolated atmosphere; and   (f) the film is exposed to fluorine for a time at least about 0.1 second up to about 2.0 seconds.   
     
     
       2. The method of claim 1 wherein said film is exposed to fluorine in an isolated atmosphere maintained under a slightly negative pressure by a vacuum means for evacuation of surplus fluorine or fluorine compounds formed in that atmosphere. 
     
     
       3. The method of claim 1 wherein the film has two sides and fluorine gas is applied in a first step to a first side thereof, and including the subsequent step of passing the second side of the film adjacent to a second pervious means having fluorine gas passing therethrough wherein the fluorine gas impinges on the second side of the film. 
     
     
       4. The method of claim 3 wherein said film is extruded into a closed container having a pair of slits therein, and said film is directed into the closed container through a first slit and emerges therefrom through a second slit. 
     
     
       5. The method of claim 1 wherein the fluorine gas is diluted with nitrogen. 
     
     
       6. The method of claim 1 wherein said pervious means is a sintered roller. 
     
     
       7. The method of claim 1 wherein said pervious means passes fluorine gas therethrough. 
     
     
       8. The method of claim 1 wherein the fluorine cross-links with polyethylene polymers to modify the surface of the film. 
     
     
       9. The method of claim 4 wherein film is first extruded and then travels along a fixed path through a set of alignment rollers and is directed into a slit for entry into a closed container surrounding said pervious means, and further including the step of controlling tension in the moving film. 
     
     
       10. The method of claim 1, wherein: (a) the film has two sides and fluorine gas is applied in a first step to a first side thereof;   (b) passing the second side of the film adjacent to a second pervious means having fluorine gas passing therethrough wherein the fluorine gas impinges on the second side of the film;   (c) wherein said film is extruded into a closed container having a pair of slits therein, and said film is directed into the closed container through a first slit and emerges therefrom through a second slit;   (d) wherein film after extrusion travels along a fixed path through a set of alignment rollers and is directed into a slit for entry into a closed container surrounding said pervious means; and   (e) controlling tension in the moving film.